The present invention relates to a measuring cell to be used in an optical measurement apparatus for measuring absorption or emission of rays in an ultraviolet or visible region to measure components in an extremely small quantity of a liquid sample.
A measuring cell for measuring absorption or emission of rays of a liquid sample in an ultraviolet or visible region has been widely used as a detecting device for accurately and quickly analyzing extremely small quantities of components, for example a capillary electrocataphoresis (CE), a high performance liquid chromatography (HPLC), a capillary electro chromatography (CEC), or a flow injection analysis (FIA) in a field of analytical chemistry, especially such as an environment analytical chemistry, a clinical field, a pharmaceutical field or the like. The measuring cell includes, generally, an introducing port for introducing a liquid sample to be analyzed, a passage of the liquid sample, and a discharging port for discharging the liquid sample, and the passage has a measuring chamber wherein the liquid sample and rays in an ultraviolet or visible region interact. The measuring cell is connected to an exit of an analytical column used in the analyzing apparatus. Also, the measuring chamber is provided with an incident window and an exit window of the measuring rays, and the rays in the ultraviolet or visible region introduced into the measuring chamber through the incident window pass through the liquid sample present in the measuring chamber, go out through the exit window, and are measured by a photometry optical system.
Recently, for example, as published in xe2x80x9cSciencexe2x80x9d, Vol. 261, p 895-897 (1993), there has been developed an electrocataphoresis device wherein a passage for introducing a liquid material and a passage for separating a liquid sample are formed on an electrocatahoresis member made of a glass base plate, for example PYREX GLASS, by using a micro-machining technique based on a semiconductor manufacturing technique. When compared with a conventional capillary electrocataphoresis device, the electrocataphoresis device has various advantages such that a high speed analysis can be made, a solvent consuming quantity is very little, a required sample is extremely small, the device can be miniaturized, and the like. These characteristics are very useful for enabling an on-sight or bed-side analysis, which can not be made by the conventional analyzing devices in the field of analytical chemistry. Also, in a field of a DNA analysis or the like, the above-mentioned advantages are useful for screening from a view point of the high speed analysis.
In the measuring cell to be used in a field of the analytical chemistry, a volume of the measuring chamber is required such that separating or analyzing ability for the various analytical methods are not impaired, i.e. the passage sectional area is generally the same as that of a separation capillary column. As the separation capillary column, generally, a molten silica capillary having an inner diameter in the order of several hundreds xcexcm is used. In order to obtain a measuring chamber having the same sectional area of the passage as that of the molten silica capillary, there has been proposed a manufacturing method of a measuring cell by joining two glass base plates provided with a passage on the surface thereof by applying the micro-machining technique.
In this case, it is important that the two base plates are securely joined and the surface of the passage is chemically stable in view of an influence on an analysis. However, in a conventional joining method employing a thermal oxidation film of an Si thin film, there may be formed a thermal stress and distortion on the base plates due to high temperature process to obtain the thermal oxidation film, so that the joining of the base plates becomes insecure and the measuring chamber can not be kept air-tightly.
Also, in case the measuring cell is desired to be used as a disposable cell, although a plastic cell is advantageous in view of its cost, it is required at the present situation that the two base plates are processed at a temperature higher than 100xc2x0 C. in a joining process thereof. Thus, it is difficult to bond the base plates while keeping the passage shape of the accurately formed plastic base plates. Also, since the surface of the plastic product mostly show hydrophobic property, there is a problem that a solution can not be easily introduced into the cell.
Also, among incident lights entering the measuring chamber, lights, i.e. stray lights, which do not interact with a liquid sample to be measured, enter a measuring device to thereby lower a measuring sensitivity.
The present invention has been made to solve the above problems, and an object of the invention is to provide a disposable measuring cell, wherein a passage of a measuring chamber has substantially the same sectional area as that of a separation capillary column; the measuring chamber has a sufficient airtightness; the inner surface of the passage is chemically stable; and stray lights do not enter a measuring device.
Another object of the invention is to provide a measuring cell as stated above, wherein the entire measuring cell is miniaturized with high accuracy to thereby produce a plurality of measuring cells at the same time and reduce its cost.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A measuring cell of the invention for attaining the above objects includes a sample introducing port for introducing a liquid sample, a passage for the introduced liquid sample, and a sample discharging port for discharging the liquid sample. At least a part of the passage is used as a measuring chamber. The measuring cell is formed of two base plates joined together by using an SiO2 thin film formed by a sputtering film forming method or the like, and a groove portion as the passage is formed on a joining surface of at least one of the two base plates. Thus, without using a high thermal process step causing a thermal stress on the base plates, joining of the glass base plates can be securely carried out. Moreover, since the inner surface of the passage is covered by the SiO2 thin film, a material of the base plates does not contact the liquid sample. Thus, the chemical and physical characteristics of the inner surface of the passage are determined by characteristics of the thin film formed thereto, so that various characteristics can be relatively easily provided to the inner surface of the passage by changing film forming conditions and compositions of the materials.
Also, in order to form a groove portion as the passage on a joining interface or surface of the base plate, a known photo-fabrication technique and a wet etching technique can be used to thereby form the groove portion with a desired width and depth less than several hundreds xcexcm in either case. Therefore, a fine passage having a passage sectional area which is substantially the same as that of the separation capillary column can be used as the measuring chamber, so that it is possible to form a measuring chamber having a fine volume to an extent which does not impair separation or analyzing abilities of the various separation analyzing devices. Further, by providing optically opaque portions on both sides of the sample passage in a flow direction of the sample through formation of the optically opaque portions, such as an Si thin film, by the sputtering method on the joining surface, stray lights which do not interact with the liquid sample to be measured do not enter the measuring device, so that the measuring cell having a high measuring sensitivity can be obtained.
In case at least one of the two base plates is made of a plastic material, a cheap disposable measuring cell can be manufactured. When the plastic material is used for the base plate, although there are problems of keeping a passage shape at the time of joining the base plates and the hydrophobic property of the surfaces, the passage shape can be easily maintained and the inner surface of the passage become hydrophilic by covering the plastic surfaces with the SiO2 thin films and joining the base plates by using means, such as a hydrofluoric acid joining or the like.
Incidentally, it is preferable that the thicknesses of the base plates are made thin as little as possible in order to suppress absorption of lights to be measured by the base plates, i.e. in a range from several hundreds xcexcm to 1 mm. Although a size of the measuring cell is not specially limited, it is desirable that the measuring chamber has a length in the order of several hundreds um not to lower its resolving power.
Also, in case a liquid sample is measured through absorption of ultraviolet rays, when ultraviolet transmittance glass having a good transmittance to an ultraviolet ray region, foe example, Product No. UV-22 manufactured by Hoya Corporation or #9741 manufactured by Corning Inc., is used as base plates to provide the above structure, a measuring cell usable for measuring light absorption in the ultraviolet ray region can be obtained. When it is desired to increase the ultraviolet ray transmittance, if the above structure is embodied by using quartz glass as the base plates, an ideal measuring cell for light absorption in the ultraviolet ray region can be obtained.